const myAtoi = function(str){
  str = str.trim();
  if(!str) return 0;
  let isPositive = 1;
  let i = 0, ans = 0;
  if(str[i] === '+'){
    isPositive = 1;
    i++;
  }else if(str[i] === '-'){
    isPositive = 0;
    i++;
  }
  for(; i < str.length; i++){
    let t = str.charCodeAt(i) - 48;
    if(t > 9 || t < 0) break;
    if(ans > 2147483647/10 || ans > (2147483647-t)/10){
      return isPositive ? 2147483647 : -2147483648;
    }else{
      ans = ans*10 + t;
    }
  }
  return isPositive? ans : -ans;
}
